Micro Flow Rate Generator, Pump and Pump System

ABSTRACT

A micro flow rate generator comprising a porous thin film placed in a channel, a pair of electrodes arranged on the opposite sides of the porous thin film, a means for supplying solution to the channel, and a DC power supply for applying a DC voltage between the pair of electrodes, characterized in that the solution has been processed so as not to cause electrolysis and a flow of the solution passing through the porous thin film is generated by applying a DC voltage between the pair of electrodes.

TECHNICAL FIELD OF THE INVENTION

The present relates to a method by which micro flow rates of liquid can be controlled, a pump using it and a pump system using it, and more particularly to a micro flow rate generator and a pump which can be suitably used for analyzing living substances, chemicals and foods, and a pump system using it.

BACKGROUND OF THE INVENTION

Control of the flow rate of liquid passing within a tube has been accomplished by a method of varying the opening or adjusting the pressure by the use of a mechanical valve. For instance, Patent Document 1 discloses a medical fluid feed device equipped with a medical fluid feed pump, which is a diaphragm pump for vibratory feeding of medical fluid from a medical fluid storage tank. Further, Patent Document 2 discloses a washing water delivery device which, equipped with bubble mixing unit for mixing bubbles into washing water, delivers a bubble flow in which a large quantity of micro bubbles are dispersed in washing water.

However, these methods are not suitable for applications in which a micro flow rate needs to be accurately controlled because they give rise to a pulsating current.

On the other hand, Patent Document 3 discloses a fluid feed device equipped with a fluid storage unit, a pressure transfer unit and an electrochemical cell unit using for its cathode an anion exchange resin as a medium of anion movement and a metal oxide, to which an electric conductor is added.

Further, Patent Document 4 discloses a method by which a micro flow rate is generated by utilizing an electro-osmotic flow or electrophoresis with a thin and long capillary tube in order to obtain a pulsation-free or low-pulsation and low-flow rate pump. For instance in FIG. 1 thereof, a case in which electrophoresis, is generated by applying, after letting in a sample solution into a quartz capillary tube through one end, a high voltage to both ends of the capillary, and the electrophoretically separated component is moved.

Further, Non-Patent Document 1 discloses an invention to generate or control the micro flow rate of a solution with a porous thin film by using a relatively low voltage from a battery or the like, instead of applying a high voltage, as a fruit of research by the inventors pertaining to the present application.

It is stated in Non-Patent Document 1 that the micro flow rate can appropriately controlled if an aqueous solution of sodium or an aqueous solution of potassium, whose level of ionization is relatively high, is used as the solution.

Patent Document 1: Japanese Patent Laid-Open No. 2000-265945

Patent Document 2: International Publication WO99/09265

Patent Document 3: Japanese Patent Laid-Open No. H09-192213

Patent Document 4: Japanese Patent Laid-Open No. H09-281077

Non-Patent Document 1: Sugitani, Hasegawa and Narumi, “Fluid characteristics of fluid passing a porous thin film when a voltage is applied”, Transactions of Lectures [No. 027-1] at the 39th General Meeting of the Hokuriku-Shinetsu Branch of The Japan Society of Mechanical Engineers, pp. 93-94, (Mar. 8, 2002)

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As attempts to control a micro flow rate, for instance, a solution containing blood, DNA, cells or the like is let flow in a microchannel, and the object is observed as enlarged by a microscope. In this case, if the flow rate of the pump fluctuates or pulsates, the enlarged image of the object will move to make accurate observation impossible. For this reason, pumps free from pulsation and fluctuation are craved for. They are also required to be free from clogging, capable of securing a stable flow rate, moreover easy to handle and inexpensive.

However, at the moment there is no pump that can fully satisfy these requirements. Especially, no conventional pump permits easy reversal of the flow direction.

For instance the method described in Patent Document 4 above to generate a micro flow rate by utilizing an electro-osmotic flow or electrophoresis with a thin tube such as a capillary tube requires a high voltage of 100 V or above, and as the flow rate that is obtained is low, the micro flow rate is difficult to control.

On the other hand, the invention described in Non-Patent Document 1 above regarding the control of the micro flow rate using a porous thin film is an invention still in an R&D stage, and involves a number of problems to be solved in making it available for practical application. One of the problems is, as an aqueous solution containing sodium or potassium is used as the working fluid, the fluctuation of flow rate characteristics due to the generation of hydrogen and bubbles when a voltage is applied.

An object of the present invention is to solve the problems noted above and provide a pulsation-free or low-pulsation micro flow rate generator, pump and pump system in whose fluid neither hydrogen nor bubbles are generated.

Another object of the invention is to provide a pulsation-free or low-pulsation micro flow rate generator, pump and pump system which can work on a relatively low voltage and permits easy flow rate control.

Still another object of the invention is to provide a micro flow rate generator, a pump and a pump system which are free from clogging, capable of securing a stable flow rate, moreover easy to handle and inexpensive.

MEANS TO SOLVE THE PROBLEMS

A characteristic of the present invention consists in a micro flow rate generator provided with a porous thin film arranged in a flow channel, a pair of electrodes installed on the two sides of the porous thin film, means of feeding a solution to the flow channel and a DC power source for applying a DC voltage between the pair of electrodes, wherein the solution is a solution so processed as not to allow electrolysis to occur; and a flow of the solution via the porous thin film is generated by applying the DC voltage between the pair of electrodes.

Another characteristic of the invention consists in that an oxidant is added into the solution as the solution so processed as not to allow electrolysis to occur.

Still another characteristic of the invention consists in that the solution so processed as not to allow electrolysis to occur is a liquid comprising a medium in which particulates of 0.01 μm to 0.5 μm in grain size are floated.

Yet another characteristic of the invention consists in a pump or a pump system using the micro flow rate generator.

In the micro flow rate generator, pump or pump system according to the invention, a porous thin film is fitted in the flow channel, and a DC voltage is applied to a pair of electrodes so arranged with the porous thin film in-between that the inlet side of the solution is the anode and the outlet side is the cathode. Since the relationship between the voltage and the flow rate therein differs with various conditions including the combination of the types, materials and other aspects of the solution, electrodes and porous thin film and the extent of ionization of the solution, the control of the micro flow rate is made possible by varying this combination. By appropriately setting these conditions, a pump which can achieve a flow rate substantially proportional to the applied voltage can be obtained.

For instance, since an aqueous solution of sodium and an aqueous solution of potassium are highly ionized, the use of one of them as the solution would make possible appropriate control of the micro flow rate, but bubbles arise as noted above. The present inventor, as a result of exhaustive research, has found that even if an electrolytic solution such as an aqueous solution of sodium or an aqueous solution of potassium is used, the generation of hydrogen or bubbles can be prevented by using a method of adding an oxidant, such as hydrogen peroxide water or potassium dichromate, into the aqueous solution, or a colloidal disperse system in which particulates are dispersed, the flow rate can be controlled with a low voltage, resulting in the successful completion of the present invention.

EFFECTS OF THE INVENTION

According to the invention, the micro flow rate generator is provided with a porous thin film arranged in the flow channel of the solution and a pair of electrodes, and a micro flow rate of the solution free from pulsation can be generated by applying a relatively low DC voltage of around 10 V between the two electrodes. This flow rate is proportional to the applied voltage and can be controlled readily, and the device is easy to handle and inexpensive. Clogging does not occur, and a stable flow rate can be secured. Namely, neither hydrogen nor bubbles are generated within the solution or the disperse system, and there is an effect that the flow rate characteristic does not change even if the operation is repeated many times.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The best modes for carrying out the present invention will be described flow. First, the basic configuration of a micro flow rate generator according to the invention will be described.

FIG. 1A is a schematic diagram illustrating the principle of the micro flow rate generator according to the invention. FIG. 1B is a perspective view showing the essential part of the micro flow rate generator according to the invention. On the way of a channel 1 in which a solution 20 is to let flow, a porous thin film 2 is fitted in a direction orthogonal to the direction of the axis of this channel via a support 3. And a pair of electrodes 4 and 5 is installed upstream and downstream with this porous thin film 2 in-between. A round opening in the support 3, namely the round are a in which the porous thin film 2 meets the flow, and the round are as bored in the pair of electrodes 4 and 5 have substantially the same radiuses, and their centers are positioned on the axis of the channel.

The solution 20 is so treated as not to let electrolysis take place. For this purpose, an oxidant is added into the solution. A zinc electrode may be used as the cathode, or a combination of such a solution and a zinc electrode may be used as well.

As another method, the solution 20 may be a liquid in which particulates of 0.01 μm to 0.5 μm in grain size are floated in a medium. In this case, the particulates need to have a property of being electrically charged in liquid. For instance, a colloidal disperse system consisting of particulates separated in a solution can be used.

To the pair of electrodes arranged with the porous thin film 2 in-between, a prescribed DC voltage of 100 V or below is applied from a DC power source 6 via a switch 7 so as to make the inlet side of the solution an anode 4 and the outlet side a cathode 5. In the illustrated case, the left side one is supposed to be the anode 4 and the right side one, the cathode 5, with the solution 20 flowing in the direction of the arrow. Incidentally, when a voltage of 10 V to 20 V is applied between the pair of electrodes, the current flowing between the electrodes is a micro current of 30 μA to 100 μA; the extremely low power consumption is one of the features of the invention.

Incidentally, as will be described in detail afterwards, the relationship between the applied voltage and the flow rate will vary with various conditions including the combination of the types, materials and other aspects of the solution, electrodes and porous thin film, which are the constituent elements, and the extent of ionization of the solution. Therefore, a pump which can control the desired flow rate with the combination of these constituent elements can be obtained.

FIG. 2 is a vertical section showing the configuration of one embodiment of a micro flow rate control pump according to the invention. The porous thin film 2 is held within a first channel 1 via the support 3. The first channel 1 and the support 3 are configured of electrically insulating materials. The porous thin film 2 is made of, for example, a nickel material of 11 μm in thickness, and 55,600 pores of about 5 μm in bore are regularly provided in a round are a of 8 mm in diameter. Further, the anode 4 and the cathode 5 are installed on the two sides of the porous thin film 2. As shown in FIG. 1B, the support 3 and the pair of electrodes holding the porous thin film 2 are flat, and are fixed to the first channel 1 with sealing materials held between them.

As will be stated afterwards, it is desirable for the bore of the pores to be in a range of 1 μm to 100 μm. Further, it is desirable for the spacing between each electrode and the porous thin film 2 to be in a range of 1 mm to 1 cm. This pair of electrodes are connected to the DC power source 6 via the change-over switch 7. The DC power source 6 is a power source for supplying the pair of electrodes with a DC voltage about 100 V or less, and a battery can be used for this purpose. Or a power source which derives DC power from an AC source via a converter may instead be used as the DC power source 6. It is supposed to be provided with voltage regulating means, such as a variable resistor. The change-over switch 7 has a function to change over the polarity of the voltage fed to the pair of electrodes or to turn it off. The inlet side pipe 27 of the first channel 1 is connected to a solution tank (not shown). The heights of the solution tank and of the first channel 1 are basically the same; namely the head is zero. As will be stated in a subsequent description of embodiments, it is also possible to achieve a desired flow rate characteristic by changing this head according to the application.

Incidentally, the round openings bored in the pair of electrodes 4 and 5 need not be the same in size as the round opening bored in the support 3. For instance, the openings bored in the pair of electrodes 4 and 5 may be greater in radius than the opening bored in the support 3 and configured as openings having a plurality of thin passages.

A second channel 10 communicating with the outlet side pipe 26 of the first channel 1 is divided into an inlet side sub-channel 8 and an outlet side sub-channel 9, and joined by a thin pipe 22. The lower part of the inlet side sub-channel 8 is filled with the solution (drive liquid) 20. On the other hand, this thin pipe 22, the upper part of the inlet side sub-channel 8 and the upper part of the outlet side sub-channel 9 are filled with an intermediate medium 21. Further, the outlet side sub-channel 9 which is on the outlet side of the pump is filled inside with a discharge liquid 23, such as water or blood, and is connected to an outlet side pipe 28.

FIG. 3 shows an example of combination of solution, porous thin film and so forth. In the example of FIG. 3, the solution (drive liquid) 20 comprises a medium of water and an electrolytic aqueous solution of sodium chloride or potassium chloride. The porous thin film 2 is made of nickel, and the electrodes are in a combination of the anode 4 made of silver and the cathode 5 made of zinc. Or if the combination of silver and silver chloride (AgCl) is adopted, they can be configured as reversible electrodes which are switched over between an anode and a cathode. To the solution, hydrogen peroxide water or potassium dichromate is added as oxidant.

The combination shown in FIG. 3 is a mere example, and it goes without saying that other elements of similar characteristics can as well be combined. For instance, a combination of a zinc plate (cathode) and a silver plate (anode) may be used for the electrodes.

Another example regarding the combination of the solution, porous thin film and so forth is shown in FIG. 4. In the example of FIG. 4, a colloidal disperse system in which particulates are dispersed is used as the solution (drive liquid) 20. Thus, the colloidal disperse system as the solution uses as the medium water or ion exchange water cleared of ions by an ion exchanger, into which polystyrene particles or silica particles are mixed. The colloidal disperse system may comprise oil into which particulates are mixed.

Further, nickel or non-metallic polycarbonate is used for the porous thin film 2. Non-metallic acryl resin can also be applied as the material of the porous thin film. The electrodes, both the anode and the cathode, are stainless steel plates. In a specific example of configuration of the porous thin film 2 made of polycarbonate, the thickness is 11 μm and 320,000 pores of about 5 μm in bore and provided in a circle of 10 mm in diameter for instance.

Incidentally, the colloidal disperse system may as well be what has particulates suspended in water or what has particulates suspended in oil or organic solvent.

What can be used as the solution (drive liquid) 20 is not limited to a colloidal disperse system. For instance, a suspension comprising particulates dispersed in ion exchange water as the medium may as well be used.

In this way, the solution (drive liquid) 20 usable in the pump according to the invention may be any liquid comprising particulates of 0.01 μm to 0.5 μm in grain size floated in a medium. In this case, any particulates, whether metallic or non-metallic, can be used if only they have a property of being electrically charged in liquid. For instance, alumina powder can be used as the particulates.

Next, the operation of the embodiment shown in FIG. 2 will be described. In the solution tank, the inside of the first channel 1 and the lower part of the inlet side sub-channel 8 of the second channel 10 are filled with an electrolytic aqueous solution (see FIG. 3) or a colloidal disperse system in which particulates (see FIG. 4) are dispersed as the drive liquid 20. And the lower part of the outlet side sub-channel 9, which constitutes the output side of the pump, is filled with the discharge liquid 23, such as water, sewage or blood.

The application of the DC voltage to the anode 4 and the cathode 5 causes the sodium aqueous solution 20 to flow to the inlet side of second channel, and it presses the intermediate medium (silicon, transformer oil or the like) 21 to force out the discharge liquid (such as water or sewage) 23 toward the outlet side pipe 28. When voltage application to the anode 4 and the cathode 5 is stopped, the flow of the solution will stop. By such an operation, the micro flow rate of the solution can be generated.

Incidentally, hydrogen and bubbles are generated in the electrolytic aqueous solution (e.g. sodium aqueous solution) 20, which is the solution by the voltage application, and affect the flow rate. However, the generation of hydrogen and bubbles can be prevented by adding an oxidant, such as hydrogen peroxide water or potassium dichromate. Use of an intensely electrolytic solution after taking such a precaution enables the flow rate to be generated by applying an even lower voltage.

The generation of hydrogen can be also prevented by a method using a colloidal disperse system.

FIG. 5 shows one result of experiment conducted to determine the flow rate characteristic of the pump on the basis of the combination of elements listed in FIG. 3 by using the micro flow rate control pump shown in FIG. 2. The sample liquid was a 0.9% saline solution, the applied voltage was 5 V and the porous thin film 2 used was a nickel foil, whose bore was 5.01 μm. The electrodes were a zinc plate (cathode) and a silver plate (anode). The height (water column) of the solution tank is 0 mm. Regarding the electrodes here, a zinc plate was used for the cathode and a silver plate for the anode. It is seen from this diagram that a flow was generated immediately after the voltage application. The experiment started in a state of a zero voltage, and a voltage of 5 V was applied when 300 seconds had passed. After the voltage application, the flow rate increased, reaching about 2.0 (mm³/s) when 350 seconds had passed, and thereafter a substantially constant flow rate was obtained continuously.

A fluid transfer device according to the invention is characterized by the absence of pulsation as a matter of principle unlike a pump which uses a diaphragm or a piston. Although some pulsation is in the flow rate data diagrammed in FIG. 5, it seems that the pulsation indicated by the data was due to the instability of the electronic balance and programmatic problems as a result of further scrutiny together with the results of other experiments we conducted subsequently. The reason is that a similar fluctuation was seen in the state before the voltage was applied (when the flow rate was zero). Therefore, pulsation attributable to the pump is likely to be less than the diagrammed data suggest. Furthermore, though the period during which a constant flow rate was stably obtained is 50 seconds according to the data, actually the constant flow rate is likely to have been stably obtained in about 5 to 10 seconds after the voltage application because there were a delay due to a programmatic problem and other factors.

We repeated experiments a number of times and confirmed the absence of hydrogen or bubbles. By using a zinc plate as the cathode, generation of hydrogen can be prevented. And by using a silver plate as the anode, corrosion of the film by chlorine can be prevented. Use of an AgCl reversible electrode as the cathode proves even more effective. Addition of hydrogen peroxide water or potassium dichromate as the oxidant provides a still greater effect.

A graph of the flow rate characteristic of the pump when the voltage is raised to 8 V is shown in FIG. 6 for the sake of comparison. At a voltage of 5 V, the flow rate was about 2.0 (mm³/s) and at a voltage of 8 V the flow rate was about 4.0 (mm³/s); when the voltage was raised, the flow rate also increased.

FIG. 7 shows the result of using a colloidal disperse system, comprising mono-disperse polystyrene particles in ion exchange water as the aqueous solution, on the basis of the combination of elements listed in FIG. 4. The sample liquid was a system of 0.01% mono-disperse polystyrene particles, the applied voltage was 5 V, and the porous thin film 2 used was a nickel foil, whose bore was about 5 μm. The electrodes, both the anode and the cathode, were stainless steel plates. Since ion-exchanged colloidal disperse system generates neither hydrogen nor chloride, stainless steel plates can be used for electrodes.

The experiment started in a state of a zero voltage, and a voltage was applied when 300 seconds had passed. It is seen from this diagram that a flow was generated immediately after the voltage application, and a substantially constant flow rate of about 1.0 (mm³/S) was obtained. The flow rate can be regulated by varying the concentration and/or the voltage.

Advantages of the colloidal disperse system include the repeated usability of the same solution because it is not electrolyzed and the non-generation of bubbles or hydrogen. This was confirmed by repeated experiments.

FIG. 8 shows an example of result of using a polycarbonate film as the porous thin film on the basis of the combination of elements listed in FIG. 4. The sample liquid was a system of 0.01% mono-disperse polystyrene colloidal disperse system, the applied voltage was 5 V, and the porous thin film 2 used was a polycarbonate film, whose bore was about 5 μm. The electrodes, both the anode and the cathode, were stainless steel plates. The experiment started in a state of a zero voltage, and a voltage was applied when 300 seconds had passed. It is seen from this diagram that a flow was generated immediately after the voltage application, and a substantially constant flow rate of about 1.0 (mm³/s) was obtained. The reproducibility of this experiment was confirmed by repetition of the experiment. Advantages of the polycarbonate film include the less susceptibility of the film to corrosion, resultant durability and the low cost.

The operating principle of the micro flow rate control pump according to the invention will be described hereupon. First, the relationship between the applied voltage and the pump flow rate will be described.

With the voltage applied to the pump being represented by V and the current by I, the input to the pump is V×I. Further, with the discharge pressure of the pump being represented by P and the flow rate by Q, the output from the pump is given by P×Q. Therefore, with the efficiency being represented by η, η=PQ/(VI)  (1) holds.

FIG. 9 shows the pump output PQ, obtained by using the pump according to the invention, relative to the pressure P. It is seen from this diagram that the pump output remains substantially constant even if the pressured is varied. The voltage V applied then was 5 volts, and the experiment showed that, even if the pressure P was varied, the current I remained substantially constant at 3×10⁻⁵ amperes. It is thus seen that, when the pump input VI=1.5×10⁻⁴ held, the pump output PQ had a constant value of about 10⁻⁸ watts. Therefore, though P varies and Q also varies correspondingly, the constant relationship of PQ=ηVI holds if the input is constant, and the efficiency η will be η=0.67×10⁻⁵ from Equation (1). On the other hand, if the pore of the radius R bored in the film of the thickness L is approximated by a micro tube of the length L and the radius R, the pressure loss P which a fluid of the flow rate Q suffers when passing this pore is given by the following equation (the flow is supposed to be a laminar flow). $\begin{matrix} {Q = {\frac{\pi\quad R^{4}}{8\quad\mu}\frac{P}{L}}} & (2) \end{matrix}$ where μ is the fluid viscosity.

FIG. 10 shows comparison of Equation (2) with experimental values. The straight denoted as Poiseuille flow in the diagram represents Equation (2) and black dots represent experimental values. They well agree with each other, indicating that the pore bored in the film can be approximated by a micro tube. A constant determined according to the device from Equation (2) is represented by C, Q=CP  (3) will hold.

Although the values of η and C vary with the actual combination of the pump and the fluid chip, if they are experimentally determined at the time of shipping, the desired flow rate Q can be figured out by providing the power VI (substantially the voltage V because the current I is actually constant) by the next Equation (4) obtain able from Equations (1) and (3). $\begin{matrix} {Q = \sqrt{\frac{\eta\quad{VI}}{C}}} & (4) \end{matrix}$

Where η and C are set to prescribed values at the time of shipping and R is also kept constant, rewriting Equation (4) from the relationship of V=RI will give the following equation. Q=k·V  (5) (Where K is a Constant)

Where η and C are set in advance from Equation (5), the flow rate Q can be regarded as being proportional to the applied voltage V.

FIG. 11 shows an example of result of measuring the pump discharge rate relative to the applied voltage by using the pump according to the invention. From this diagram, too, it is seen that the flow rate Q in the pump according to the invention is substantially proportional to the applied voltage V except in the region where the flow rate Q is small.

Generally, it is difficult to use a micro flow rate pump while directly measuring the flow rate Q with a flow rate meter. Therefore, in order to secure an accurate set flow rate for a micro flow rate pump, it is desirable to acquire by experiment in advance a characteristic diagram giving the relationship between the applied voltage V and the flow rate Q like FIG. 11, control the voltage along this characteristic diagram and obtain the prescribed flow rate.

Next will be described the point that the flow rate Q proportional to the applied voltage V is obtained with the pump according to the invention.

In the pump according to the invention, the water level of the solution tank, namely the head, may be zero. The phenomenon that a flow arises from the plus pole to the minus pole when the head is zero seems mainly attributable to an electro-osmotic flow or electrophoresis.

Then, when the impact only of the voltage when the head was zero was examined, it was found that a flow rate was generated in a state in which the porous thin film was put on. This seems to be a phenomenon peculiar to a flow in the micro region because no flow rate is generated in a state in which the film is not put on. In this connection, the principle of generation of a flow rate by the application of a voltage with electrodes provided before and behind micro pores in the porous thin film will be considered below.

An electro-osmotic flow means a phenomenon in which an electric double layer is formed in a flow channel, such as a micro tube, and that double layer is moved toward the minus pole by the Coulomb force to generate a flow in one direction.

FIG. 12 is a schematic diagram of an electro-osmotic flow in a case in which the pump according to the invention uses an aqueous solution of electrolyte (sodium chloride or potassium chloride). As shown in FIG. 12, the wall face of the flow channel in the micro tube is negatively charged, and this causes plus ions to gather on and around the wall face to form an electric double layer. That electric double layer is moved toward the minus pole by the Coulomb force. The plus ions around successively move toward the wall face to form an electric double layer all the time. Also, around the electric double layer, minus ions also move, pulled by the plus ions of the electric double layer. As forces including an electrostatic force also work then, a flow is generated toward the minus pole on the whole.

This is considered the cause of the pump effects according to the invention when the aqueous solution of electrolyte shown in FIG. 3 is used, especially the effect of allowing a constant flow rate to be discharged and sucked.

Next, the reason for the generation of the pump effects in the pump according to the invention by the colloidal disperse system shown in FIG. 4 seems to be as described below.

Generally, an object soaked in liquid is negatively charged in most cases, and attracts (adsorbs) plus ions in the solution. While colloid particles are also negatively charged, plus ions in the liquid are attracted around them, and the whole particles become similar to particles charged with plus ions. Then, for the sake of simplicity, colloid particles having attracted plus ions will be depicted as shown in FIG. 13.

The case of a colloidal disperse system is substantially similar to that shown in FIG. 12. However, in the case of a colloidal disperse system, plus charges stick around the minus charged particles, becoming apparently plus particles on the whole, and those plus particles are considered to give rise to a flow in a phenomenon peculiar to a micro region, such as an electro-osmotic flow, electrophoresis or adsorption. Thus in a colloidal disperse system, there are no minus particles, but a flow is expected to arise in a state such as the one shown in FIG. 14.

Next, FIG. 15 shows flow rate characteristics in a case in which the pump according to the invention uses colloid particles of 0.1 μm in diameter where the bore of the pores in the porous thin film 2 is altered but other conditions are unchanged. The applied voltage is 5 V. Four different bores of the pores were tested including 2 μm, 5 μm, 12 μm, and 40 μm. At the bores of 2 μm and 5 μm, substantially the same pump effects were obtained. However, at the bore of 12 μm, the flow rate somewhat dropped and at the bore of 40 μm, it was confirmed that no pump effects would arise. In this connection, while the bore becomes extremely large, it will be a case of absence of the film (bore), and we have experimentally confirmed that no pump effects arise in this case. Conversely, when the bore becomes extremely thin, no pump effects arise either. These findings indicate that the bore of pores, though requiring a suitable size relatively to the diameter of colloid particles, should be neither too large nor too small.

We confirmed the following points by experiment. As an example, when the colloid particles have a diameter R=0.09 μm, the porous thin film 2 has a height H=13 mm and the number of pores=55,600 in FIG. 16, it is desirable for the film thickness D=10 Mm and the bore E of the pores=5 μm in the porous thin film 2.

Further as a result repeated experiments, it was found likely that the film thickness D was in a relationship of inverse proportion to the flow rate, that the range of E=(10 to 200)R was effective and that the film thickness D was effective in the range of D=(⅕ to 2)E. For practical purposes, it is desirable for the thickness of the porous thin film to be in the range of 5 μm to 200 μm.

Further, the gaps between the pair of electrodes and the porous thin film 2 also have a significant impact on the characteristics. If the gaps are too narrow, the electric resistance between the pair of electrodes will become small to let too large a current flow. Conversely, if the gaps are too wide, electric fields of a sufficient intensity cannot be generated for the portions of the solution before and behind the porous thin film 2, making it impossible to secure the target flow rate. For these reasons, it is desirable for the gaps between the pair of electrodes and the porous thin film 2 to be in the range of 1 mm to 1 cm.

To add, these ranges of numerical values including the film thickness D, the bore of pores and the gap between electrodes are similarly effective in the case of a solution in which fine powder is mixed into a suspension or an aqueous solution of electrolyte.

A case in which colloid particles pass micro pores (herein after referred to as simply pores) bored in the porous thin film 2 are shown in a simplified form in FIG. 17A through FIG. 17C. The horizontal linear parts in each figure represent the section of the pore in the porous thin film, and the negative charges on the interface with the liquid are indicated by minus signs. The colloid particles having adsorbed plus ions as shown in FIG. 13 are adsorbed by this interface. Minus and plus electrodes are placed to the left and right of the film in this state. Where the bore of the pores is too small relative to the colloid particles as shown in FIG. 17A, the colloid particles try to move toward the negative electrode, but are unable to pass the pores, resulting in a failure to generate the pump effects.

Where the bore is appropriate as shown in FIG. 17B, the colloid particles pass the pores and, accompanied by the portions of the liquid around them, move toward the negative electrode. On this occasion, the colloid particles already adsorbed by the interface between the film or pores and the liquid perform an action to inhibit the colloid particles having passed the pores from flowing back (blocking action). Therefore, the pump effects are generated.

Where the bore of the pores is too large as shown in FIG. 17C, though the colloid particles near the center of each pore move toward the negative electrode, the blocking action by the colloid particles on the interface is invalidated by the excessive size of the pores, a reverse flow of the colloid particles occurs between the center of the pore and the interface, resulting in a failure to generate the pump effects.

On the basis of the cause for the generation of the pump effects described above, the pump effects will arise even if the pores in the film are large in bore if colloid particles having a large diameter are used, and the flow rate then generated will also be large. Further by choosing a combination of highly adsorptive particles and film, the pump effects can be improved.

Next, regarding a colloidal disperse system containing particles, general-purpose usefulness was confirmed under many different conditions. The results of this study are described below.

FIG. 18 shows the flow rate characteristic in a case where a colloidal disperse system containing polystyrene particles was used as the drive liquid and the combination of electrodes was altered. Cases of stainless steel (anode) and stainless steel (cathode), silver (anode) and stainless steel (cathode), and silver (anode) and zinc (cathode) were tested, and it was found that the flow rate characteristic was almost the same.

FIG. 19 shows the result of a case where a colloidal disperse system containing polyethylene particles was used as the drive liquid and the filling ratio of the polyethylene particles was varied in the range of 0.1% to 0.0001%. Though the flow rate somewhat decreased at 0.0001%, substantially the same flow rate was achieved at any higher filling ratio.

FIG. 20 shows the result of a similar experiment to

FIG. 19 except that the particles were altered to silica particles. As in the case of FIG. 19, though the flow rate somewhat decreased at a filling ratio of 0.0001%, substantially the same flow rate was achieved at any higher filling ratio.

In the case of a solution of an electrolyte such as sodium or potassium and in the case of the above-described colloidal disperse system, the preferable range of the bore of the pores in the porous film was 1 μm to 100 μm, while it is considered appropriate to use particles of a diameter in the range of 0.01 μm to 0.5 μM.

FIG. 21 is a configurational diagram of another embodiment of a second channel 4 part of the pump, wherein the intermediate medium 21 is placed in the middle part of one pipe (glass tube or the like) and the discharge liquid 23 is forced out from left to right in the illustration of FIG. 21. The impact of any head difference can be disregarded for this thin pipe 26. In this way, by using the generation of a flow by the application of a voltage as the power source, pumps of various forms can be realized.

FIG. 22 and FIG. 23 are configurational diagrams of other embodiments of the pump according to the invention. In this example, the anode and the cathode to apply a DC voltage are switched over from one to the other in the micro flow rate generator shown in FIG. 2 to make reciprocation of the fluid. In this case, the use of a colloidal disperse system as the fluid for use in the driving part makes possible reciprocation of the fluid. In FIG. 22, the flow of colloid arises in the direction of the arrows, namely from the anode toward the cathode, to push the intermediate medium 21 rightward, and discharges the discharge liquid 23 through the pipe 28. At the time, a valve 34 prevents the discharge liquid 23 from flowing toward a feed tank 33. On the other hand, the flow arises in the completely reverse direction in the case shown in FIG. 23, wherein the intermediate medium 21 is pulled and the discharge liquid 23 in the feed tank 33 is fed into a linking pipe 31. At the time, the discharge liquid 23 on the discharge side is prevented by a valve 35 from being sucked through the pipe 28. In this way, suction and discharging are enabled to make possible continuous use for a long period.

Next, applications of the micro flow rate pump according to the invention shown in FIG. 1A, FIG. 1B and FIG. 2 will be described.

First, FIG. 24 is a plan of one embodiment of a pump system to which the invention is applied, and FIG. 25 shows an A-A section thereof.

A pump system 200 has a pump 100 mounted on a base 201. This pump 100 is configured in a planar shape. This is because, when the planar base 201 is mounted on the plane of a desk, the planar structure of the pump 100 would facilitate assembling. The pump 100 consists of an upper frame 101 and a lower frame 102, and a casing 103 is mounted on the top of the upper frame 101. The micro flow rate generator 106 shown in FIG. 1A, FIG. 1B and FIG. 2 is built into this casing 103. What is important here in the configurational aspect is that the plane of the porous thin film 2 in the micro flow rate generator 106 and the plane of the upper frame 101 should be arranged in the same direction. In this way, the device can be easily fabricated, and the number of bends on the flow channel of the solution can be reduced. Within the upper frame 101 is provided a passage 110, which communicates with links 109 and 111. When a DC voltage is applied to the pair of electrodes of the micro flow rate generator 106, the solution passes an inlet pipe 104 and an expanded path 107 and, via the micro flow rate generator 106, is discharged to its destination from an outlet pipe 105 past an expanded path 108, the linking port 109, the passage 110 and the linking path 111. The passage 110, though provided in the upper frame 101, may as well be disposed on the upper face of the lower frame 102. The separated configuration the upper frame 101 and the lower frame 102 is intended to facilitate machining of the passage 110. Of course, the upper frame 101 and the lower frame 102 may as well be structured integrally.

The pump 100 configured in this way is mounted on the planar base 201, and a battery 117, a voltage regulator (variable resistor) 116, an on/off switch 115 and a battery housing lid 118 are arranged on this base 201. The voltage regulator 116 is connected to a controller (not shown). Within the controller, the applicable voltage for the required flow rate is calculated from the data of preset conditions and the relationships expressed in Equations (4) and (5) as described above, and control is so effect as to secure the prescribed flow rate by adjusting the voltage regulator to achieve this voltage.

Incidentally, the user may as well reference the characteristics shown in FIG. 11 and directly manipulate the voltage regulator 116.

As this micro flow rate generator 106 has a feature that it can transport the solution with low-voltage power from a battery or the like, it can be driven with dry cells, but requires no separate large power source. For this reason, it is possible to build all of the battery 117, the resistor 116 and the switch 115 into the base 201 to configure the device in a readily portable form. The voltage generated by the battery 117 can be applied to the electrodes (anode and cathode) of the micro flow rate generator 106 by way of lead wires 112, 113 and 114, and this voltage can be adjusted with the resistor 116 intervening on the lead wire 114 and can be cut off the power source by the switch 115.

FIG. 26 is a configurational diagram of another embodiment of the pump system according to the invention. This case illustrates one method of contact coupling between the solution 20 as the drive liquid and the discharge liquid 23. A tank 202 is provided at the outlet of the outlet pipe 105 of the pump 100, and a partitioning wall 220 is disposed within it. With the partitioning wall 220 as the boundary, the output end of the outlet pipe 105 is connected in the left side space, and a tank 203 equipped with bellows 214 is connected to the right side space of the partitioning wall 220 via a pipe 213, a valve 211 and a pipe 212. This tank 203 contains the discharge liquid 23, and by pressing the bellows 214 this discharge liquid 23 is fed into the tank 202 via the pipe 212, the valve 211 and the pipe 213; its feeding can be stopped by closing the valve 211 subsequently. A pipe 207 is connected to the left side of this tank 202, and the discharge liquid 23 in the tank 202 is discharged into a separately installed tank 205 via a valve 208 and a pipe 206.

When a voltage is applied to the pair of electrodes of the micro flow rate generator 106 disposed in the casing 103 of the pump 100, the drive liquid 20 in a tank 204 is sucked via a pipe 217, passes the passage 110 in the upper frame 101, further passes the pipe 105 to enter a small chamber to the left of the tank 202. This solution enters a small chamber on the right side past pores in the partitioning wall 220, and pushes upward the discharge liquid 23 provided above it. This causes the discharge liquid 23 to be discharged into the tank 205 past the pipe 206. When the specific gravity of the discharge liquid is smaller than the specific gravity of the solution, they can be brought into contact with each other in the small chamber to the right of the tank 202 as illustrated. If the specific gravity of the solution 20 is smaller than that of the discharge liquid 23, they can be brought into contact with each other in the small chamber to the left of the tank 202. In the case of a solution in which the solution 20 and the discharge liquid 23 mix with each other, another intermediate medium (e.g. silicon oil) 21 can be placed intervening on the interface between them.

FIG. 27 is a configurational diagram of another embodiment of the pump 100 according to the invention. Whereas this is configured by putting the intermediate medium 21 in the passage 110 of the embodiment shown in FIG. 25 and, with the medium as the boundary, putting the drive liquid on the side of the micro flow rate generator 10 and the solution 23 on the other side, as a way to put in this solution 23 a thick pipe 119 with a valve 120 is disposed above the upper frame 101 and, after letting the solution 23 into this pipe 119, the valve 120 is closed at the time of testing.

FIG. 28 is a configurational diagram of another embodiment of the pump 100 according to the invention. This is configured by disposing the tank 204 above the input pipe 104 communicating with the casing 103, this tank 204 is filled with the drive liquid 23, and the drive liquid is introduced by gravity into the passage 110 via the pipe 104 and the micro flow rate generator 106. After that, the discharge liquid 23 is discharged to its destination from the outlet pipe 105 via the intermediate medium 21. While this flow rate varies with the height of the tank 204 provided above the micro flow rate generator 106, as a method to control the flow rate then, the way of applying the voltage to the electrodes of the micro flow rate generator 106 is adjusted. When the flow rate is to be further raised, it can be increased by applying a voltage in the forward direction. On the other hand, when the flow rate is to be reduced, a voltage in the backward direction can be applied to achieve an action in the direction of stopping the flow rate. By increasing the backward voltage, the flow can be stopped safely.

FIG. 29 is a configurational diagram of another embodiment of the pump according to the invention. This is configured by disposing a blocking unit 101-a on the way of the passage 110 and, with this unit as the boundary, pipes 122 and 123 are provided in the lower frame 102 and a long pipe 121 is arranged between them to constitute a closed loop. A pipe 124 is connected in a branched form to part of the long pipe 121 constituting this closed loop, and the inside is filled with the discharge liquid 23 via a valve 125. Also, the intermediate medium 21 is inserted on the way of the pipe 122. In this way, a desired flow rate can be achieved for a long time without having to stop the flow. In this embodiment, disposing the tank 202 having the partitioning wall 220 shown in FIG. 26 in place of the long pipe 121 could provide a similar effect.

FIG. 30 is a configurational diagram of another embodiment of the pump according to the invention. Similarly to FIG. 29, a blocking unit 110 is disposed on the way of the passage 110 and, with this unit as the boundary, the pipes 122 and 123 are provided in the lower frame 102 and connected in a U shape, and its inside is filled with the intermediate medium 21. A valve 126 is provided in part of the pipe 122, and the solution (drive liquid 20) is put in via the valve, while a valve 127 is provided in part of the pipe 123 and the discharge liquid 23 is put in via the valve. Although the upper ends of the pipes 122 and 123 are fitted to the upper part of the upper frame 101 and the valves 126 and 127 are fitted to their upper ends in this drawing, branch pipes may be disposed as well on part of the U-shaped pipes 122 and 123 fitted to the lower frame 102 and the valves 126 and 127 fitted thereto.

The pump and the pump system according to the invention so far described can be suitably used for analyzing living substances, chemicals and foods.

FIG. 31 shows the pump system according to the invention incorporated into an analyzing system for blood or the like. The analyzing system shown in FIG. 31 is equipped with, in addition to the pump system according to the invention, an analyzer 300 having a computer and its display unit 302 and microscope 304. A micro channel, disposed on the discharge side of the micro flow rate pump 100, and a visualizing function unit 310 are combined with each other, and a solution containing blood, DNA, cells or the like as the object of analysis is let flow in the micro channel, and the object is made visible by operating fluorescence or the like. And it is enlarged with the microscope 304 and observed. In this case, if the flow rate of the pump fluctuates or pulsates, the enlarged image of the object will move to make accurate observation impossible. By using the pump according to the invention, the enlarged image of the object will not move and its accurate observation is thereby made possible because the flow rate of the pump is free from fluctuation and pulsation. Moreover, while the conventional pump does not allow ready reversing the flow, this pump permits reversing the flow in a simple procedure of altering the polarities of electrodes.

In addition to the absence of fluctuation and pulsation and the ready reversibility of the flow, this pump further has the following features.

(1) The flow rate can be easily and freely controlled by varying the voltage.

(2) It excels in safety because it operates on a low voltage.

(3) It is inexpensive.

(4) It is compact.

(5) It is free from clogging and permits securing of a stable flow rate.

Because of the foregoing description, the pump according to the invention can contribute to dramatically expand the feasible ranges of experiments and research in bio-science. It can also be incorporated into various medical apparatuses for effective use.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram illustrating the principle of the micro flow rate generator according to the present invention.

FIG. 1B is a perspective view showing the essential part of the micro flow rate generator according to the invention.

FIG. 2 is a configurational diagram of one embodiment of a micro flow rate generator according to the invention.

FIG. 3 is a diagram showing an example of combination of solution, porous thin film and so forth for use in one embodiment of the invention.

FIG. 4 is a diagram showing another example of combination of solution, porous thin film and so forth for use in one embodiment of the invention.

FIG. 5 is a diagram showing an example of flow rate characteristic according to the invention.

FIG. 6 is a diagram showing another example of flow rate characteristic according to the invention.

FIG. 7 is a diagram showing still another example of flow rate characteristic according to the invention.

FIG. 8 is a diagram showing yet another example of flow rate characteristic according to the invention.

FIG. 9 is a diagram showing the pump output PQ, obtained by using the pump according to the invention, relative to the pressure P.

FIG. 10 is a diagram showing comparison of Equation (2) with experimental values.

FIG. 11 shows an example of result of measuring the pump discharge rate relative to the applied voltage by using the pump according to the invention.

FIG. 12 is a schematic diagram of an electro-osmotic flow in a case in which the pump according to the invention uses an aqueous solution of electrolyte (sodium chloride or potassium chloride).

FIG. 13 shows colloid particles having adsorbed plus ions.

FIG. 14 shows a state of flow in a case in which the pump according to the invention uses a colloidal disperse system.

FIG. 15 is a diagram showing flow rate characteristics in a case in which the pump according to the invention uses colloid particles of 0.1 μm in diameter where the bore of the pores in the porous thin film is altered but other conditions are unchanged.

FIG. 16 is a diagram showing the relationship among the diameter R of colloid particles, the bore E of micro pores and the film thickness D.

FIG. 17A is a diagram illustrating a state in which colloid particles pass micro pores bored in the porous thin film.

FIG. 17B is a diagram illustrating a state in which colloid particles pass micro pores bored in the porous thin film.

FIG. 17C is a diagram illustrating a state in which colloid particles pass micro pores bored in the porous thin film.

FIG. 18 is a diagram showing another example of flow rate characteristics of the pump according to the invention.

FIG. 19 is a diagram showing still another example of flow rate characteristics of the pump according to the invention.

FIG. 20 is a diagram showing yet another example of flow rate characteristics of the pump according to the invention.

FIG. 21 is a diagram showing a modified version of the pump according to the invention.

FIG. 22 is a diagram showing the configuration of another embodiment of the pump according to the invention.

FIG. 23 is a diagram showing one operation of the pump shown in FIG. 22.

FIG. 24 is a diagram showing a plan of one embodiment of the pump system according to the invention.

FIG. 25 is a diagram showing shows the A-A section of FIG. 24.

FIG. 26 is a diagram showing the configuration of another embodiment of the pump system according to the invention.

FIG. 27 is a diagram showing the configuration of another embodiment of the pump unit in the pump system according to the invention.

FIG. 28 is a diagram showing the configuration of another embodiment of the pump unit in the pump system according to the invention.

FIG. 29 is a diagram showing the configuration of another embodiment of the pump unit in the pump system according to the invention.

FIG. 30 is a diagram showing the configuration of another embodiment of the pump according to the invention.

FIG. 31 is a diagram showing an example of application of the pump system according to the invention.

EXPLANATION OF SIGNS

-   -   1 First channel     -   2 Porous thin film     -   3 Support     -   4 Electrode     -   5 Electrode     -   6 DC power source     -   7 Switch     -   8 Inlet side sub-channel of second channel     -   9 Outlet side sub-channel of second channel     -   10 Second Channel     -   20 Solution (drive liquid)     -   21 Intermediate medium     -   22 Thin pipe     -   23 Discharge liquid     -   26 Outlet side pipe of first channel     -   27 Inlet side pipe of first channel     -   100 Pump     -   101-a Blocking unit     -   102 Lower frame     -   103 Casing     -   104 Inlet pipe     -   105 Outlet pipe     -   106 Micro flow rate generator     -   107 Expanded path     -   108 Expanded path     -   109 Linking port     -   112 Lead wire     -   115 Switch     -   116 Resistor     -   117 Battery     -   200 Pump system 

1. A micro flow rate generator comprising: a porous thin film arranged on a flow channel; a pair of electrodes installed on the two sides of the porous thin film; a unit for feeding a solution to said flow channel; and a DC power source for applying a DC voltage between said pair of electrodes, wherein said solution is a solution so processed as not to allow electrolysis to occur, and wherein a flow of said porous thin film is generated by applying the DC voltage between said pair of electrodes.
 2. The micro flow rate generator according to claim 1, wherein an oxidant is added into said solution.
 3. The micro flow rate generator according to claim 2, wherein said electrodes are reversible electrodes.
 4. The micro flow rate generator according to claim 1, wherein said solution is a liquid comprising a medium in which particulates of 0.01 μm to 0.5 μm in grain size are floated.
 5. The micro flow rate generator according to claim 4, wherein said solution is a colloidal disperse system comprising a liquid in which particulates are dispersed.
 6. A micro flow rate generator comprising: a porous thin film arranged in a flow channel; a pair of electrodes installed on the two sides of the porous thin film; a unit for feeding a solution to said flow channel; and a DC power source for applying a DC voltage between said pair of electrodes; wherein the thickness of said porous thin film is 5 μm to 200 μm; and wherein the gap between said porous thin film and each of said electrodes is 1 mm to 10 mm.
 7. The micro flow rate generator according to claim 6, wherein said solution is a colloidal disperse system and, when the bore of pores in said porous thin film is represented by E and the diameter of colloid particles by R, said E=(10 to 200)R holds and, when the film thickness is represented by D, D is in the range of (⅕ to 2)E.
 8. A micro flow rate generator flow channel comprising: a porous thin film arranged in a flow channel; a pair of electrodes installed on the two sides of the porous thin film; a unit for feeding a solution to said flow channel; a DC power source for applying a DC voltage between said pair of electrodes; and a voltage regulating means of regulating the voltage of said DC power source; wherein said solution is a solution so processed as not to allow electrolysis to occur, and wherein the flow rate of said solution via said porous thin film can be regulated by causing said voltage regulating means to apply a DC voltage between said pair of electrodes.
 9. A pump so configured as to have an intermediate medium intervene on the downstream side of the micro flow rate generator according to claim 1, to fill the downstream side with the intended discharge liquid and to enable the discharge liquid to be delivered.
 10. The pump according to claim 9, wherein the intended discharge liquid is discharged from a feed tank communicating with an outlet pipe by applying or stopping said voltage or reversing the polarities of the anode and the cathode.
 11. The pump according to claim 9, wherein the structure of said pump is such that it has a member comprising a passage within a planar frame, wherein a casing is disposed on the input side thereof, wherein inside the casing, the horizontal face of the porous thin film and the horizontal face of the planar frame are arranged in the same direction, and an input pipe for the solution and an output pipe for the discharge liquid disposed on the side of the passage contrary to the casing are provided in this casing.
 12. The pump according to claim 11, wherein an intermediate medium is disposed to intervene in part of said passage.
 13. The pump according to claim 11, comprising a filling inlet for the discharge liquid, the inlet being part of said passage and disposed in part of the passage farther downstream than the intermediate medium.
 14. The pump system according to claim 11, wherein a DC power source for generating a voltage is coupled to the electrodes provided on the two sides of said porous thin film via lead wires.
 15. The pump system according to claim 11, wherein a control mechanism capable of regulating the voltage is provided between said electrodes and said DC power source.
 16. A pump system provided with the pump according to claim 9, wherein, in a head tank disposed on the input side of the micro flow rate generator to enable the discharge liquid to be discharged via the outlet pipe by utilizing gravity via the passage of the pump, a reverse voltage is applied to the electrodes of the micro flow rate generator and the flow rate can be controlled by regulating that voltage.
 17. The pump system according to claim 9, wherein said pump is mounted on a base, and said DC power source and a control mechanism capable of controlling the voltage of the power source are disposed on or in the base.
 18. An analyzing device comprising said pump according to claim 9 and a microscope, wherein a micro channel disposed on the discharge side of the pump for generating said micro flow rate and a visualizing function unit are combined with each other, and a solution which is the object of analysis is let flow in said micro channel to visualize the object and is observed with said microscope. 